The fimbrial adhesin F17-G of enterotoxigenic Escherichia coli has an immunoglobulin-like lectin domain that binds N-acetylglucosamine

Authors

  • Lieven Buts,

    1. Department of Ultrastructure, Institute for Molecular Biology, Vrije Universiteit Brussel, Vlaams Interuniversitair Instituut voor Biotechnologie (VIB), Brussels, Belgium.
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    • LB and JB are joint first authors.

  • Julie Bouckaert,

    1. Department of Ultrastructure, Institute for Molecular Biology, Vrije Universiteit Brussel, Vlaams Interuniversitair Instituut voor Biotechnologie (VIB), Brussels, Belgium.
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    • LB and JB are joint first authors.

  • Erwin De Genst,

    1. Department of Ultrastructure, Institute for Molecular Biology, Vrije Universiteit Brussel, Vlaams Interuniversitair Instituut voor Biotechnologie (VIB), Brussels, Belgium.
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  • Remy Loris,

    1. Department of Ultrastructure, Institute for Molecular Biology, Vrije Universiteit Brussel, Vlaams Interuniversitair Instituut voor Biotechnologie (VIB), Brussels, Belgium.
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  • Stefan Oscarson,

    1. Department of Organic Chemistry, Arrhenius Laboratory, Stockholm University, Stockholm, Sweden.
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  • Martina Lahmann,

    1. Department of Organic Chemistry, Arrhenius Laboratory, Stockholm University, Stockholm, Sweden.
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  • Joris Messens,

    1. Department of Ultrastructure, Institute for Molecular Biology, Vrije Universiteit Brussel, Vlaams Interuniversitair Instituut voor Biotechnologie (VIB), Brussels, Belgium.
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  • Elke Brosens,

    1. Department of Ultrastructure, Institute for Molecular Biology, Vrije Universiteit Brussel, Vlaams Interuniversitair Instituut voor Biotechnologie (VIB), Brussels, Belgium.
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  • Lode Wyns,

    1. Department of Ultrastructure, Institute for Molecular Biology, Vrije Universiteit Brussel, Vlaams Interuniversitair Instituut voor Biotechnologie (VIB), Brussels, Belgium.
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  • Henri De Greve

    Corresponding author
    1. Department of Ultrastructure, Institute for Molecular Biology, Vrije Universiteit Brussel, Vlaams Interuniversitair Instituut voor Biotechnologie (VIB), Brussels, Belgium.
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E-mail hdegreve@vub.ac.be; Tel. (+32) 2 629 19 11; Fax (+32) 2 629 19 63.

Summary

The F17-G adhesin at the tip of flexible F17 fimbriae of enterotoxigenic Escherichia coli mediates binding to N-acetyl-β-d-glucosamine-presenting receptors on the microvilli of the intestinal epithelium of ruminants. We report the 1.7 Å resolution crystal structure of the lectin domain of F17-G, both free and in complex with N-acetylglucosamine. The monosaccharide is bound on the side of the ellipsoid-shaped protein in a conserved site around which all natural variations of F17-G are clustered. A model is proposed for the interaction between F17-fimbriated E. coli and microvilli with enhanced affinity compared with the binding constant we determined for F17-G binding to N-acetylglucosamine (0.85 mM−1). Unexpectedly, the F17-G structure reveals that the lectin domains of the F17-G, PapGII and FimH fimbrial adhesins all share the immunoglobulin-like fold of the structural components (pilins) of their fimbriae, despite lack of any sequence identity. Fold comparisons with pilin and chaperone structures of the chaperone/usher pathway highlight the central role of the C-terminal β-strand G of the immunoglobulin-like fold and provides new insights into pilus assembly, function and adhesion.

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